As part of the move to Python3, the testsuite is now designed
to work with a virtual environment.
This change is to have runTestsuite use the venv method if
possible and fall back if it can't. If the script is run from
an externally activated virtual enviroment, then use that and
don't try either method.
Change-Id: I9724c446d67a5ee9e550644e4a78739de823536e
ee85895d88